This invention relates to improvements in office chairs and more specifically to improvements to adjustment and control systems for the various movable and for shapable parts of an office chair.
It is known to use a pneumatically operated adjustment mechanism in chairs. The adjustment results from telescopic engagement between two portions actuated by a jack. Preferably, the pneumatic system includes a cartridge or "jack" containing a compressed gas feeding two coaxial cylinders embodying the two portions, the control of communication between the cylinders being provided by opening or closing a control valve. Such a system is described, for example, in the French Patent No. 2,025,110.
It is also known to allow a tilting of the back portion upon the seat portion. The tilting is lockable in each of two end positions or in one of a series of intermediate positions.
It is also known to allow an adjustment of the tilting tightness or tension of the chair, i.e. of the seat portion and/or of the back portion. For example, by using a twisting spring wound around the tilting shaft, the adjustment resulting from the twisting torque is applied to the spring. A typical mechanism of this kind makes use of the position of a translating movable element.
All such adjustment and control possibilities offer to the user a maximal comfort whatever his size, his conformation and the conditions of use of the chair. Most of them however have the drawback to be independent and distributed in various locations under the seat, which requires from the user a good deal of trial and error when he wants to select the adjustment he wants to act upon.
There exist indeed already chairs in which some controls are grouped or coupled with a view to be acted upon a reduced member of control members.
For example, each of the document WO 81/03605 and the French Patent No. 2,460,648 disclose an armchair in which the height adjustment of the seat and the tilt adjustment of the back are controlled through an unique rotative member, i.e. a cam, which act, depending upon its angular position, upon one or the other of two valves equipping two pneumatic cylinders controlling the adjustments. This control member being unique, it does not provide the user with a differentiation between said two adjustments.
European Patent No. 0,385,473 discloses a chair having systems for adjusting the height and the tilting tension, the systems being controlled through two distinct organs located at the same place. However, there does not exist means for adjusting the degree of tilt which, if they would be coupled with the adjustment systems, could be actuated at the same place under the seat. European Patent No. 0,592,008, which is a division of the precedent, has the same limitations. In both last documents, the mechanism is extremely complicated.
Reversely, European Patent No. 0,549,026 discloses a chair having a mechanism which can be called "global" but very simple to control at will the seat height and the back tilting. The mechanism comprises an activation lever designed to take different positions in which, through proper linkages, it gives various configurations to the chair elements, somewhat like shifting gears lever. It is therefore not really a control for different adjustments.
It appears therefore that, in the prior art, a number of attempts have been made to allow a seat user to proceed with the various possible adjustments of said seat through organs grouping or coupling several controls together, but that none of such adjustment mechanisms have been designed for the three said adjustments with a differentiation of the adjustment controls.